In recent years, self-luminous organic electro-luminescence (EL) display devices have been actively studied as display devices that can achieve high brightness while being of the thin type. An organic EL element has a structure in which an organic layer serving as a light emitting layer is sandwiched between opposing electrodes, and the light emission is controlled by on/off of the current to the electrodes, thereby forming a display device. The display devices are classified into a passive matrix type and an active matrix type. The former is used as a backlight or a relatively low definition display device and the latter is used as a relatively high definition display device such as a television or a monitor.
In organic EL elements forming such organic EL display devices, a large problem is that an organic layer has a short lifetime which serves as a light emitting layer. Although the light emission time has been increasing through various studies in recent years, the current element lifetime is still short when used, for example, for a television or a monitor, and the brightness is reduced by half in 2000 to 3000 hours in the case of continuous lighting. As a reason for the short element lifetime, invasion of moisture into the organic layer serving as the light emitting layer or thermal destruction due to heating after formation of the organic layer or due to heat generation of the element is notable, and various improvements have been improved.
Organic EL light emitting elements of this type are described in Japanese Unexamined Patent Application Publication (JP-A) No. H10-275680 and Japanese Unexamined Patent Application Publication (JP-A) No. 2002-343559 (hereinafter referred to as Patent Document 1 and Patent Document 2). Among them, Patent Document 1 discloses the organic EL light emitting elements having a protective film in the form of a multilayer structure including two layers, i.e. an organic layer and a metal layer, or two layers, i.e. an inorganic layer and a metal layer.
On the other hand, Patent Document 2 discloses an organic EL light emitting layer in which a heat dissipating plate of metal is provided as a heat dissipating member on one of electrodes forming an organic EL element, through an adhesive layer.
In Patent Document 1, when the two layers including the organic layer and the metal layer are employed as the protective film, a problem arises that the thermal conductivity of the organic layer is low and thus the heat generated in the element cannot be sufficiently dissipated or radiated. On the other hand, in the case of the two layers including the inorganic layer and the metal layer, when use is made of SiO2 cited in the Document as an example of a semiconductor compound forming the inorganic protective film, a problem is that the thermal conductivity of SiO2 is low and thus the heat generated in the element cannot be sufficiently dissipated or radiated and, further, it is not possible to sufficiently prevent invasion of moisture as the protective film.
According to Patent Document 2, the problem of heat dissipation can be avoided, but a problem has arisen that a space is formed at a separation portion between light emitting elements in the form of a passive matrix structure and an organic solvent or moisture generated from an adhesive remains at this portion or the adhesive enters this portion, and thus the light emitting layer protection, which is most important, cannot be securely achieved, thereby reducing the element lifetime.
Further, a problem has arisen that since a method of forming the foregoing protective film is generally performed at a temperature that does not decompose an organic layer, it is not possible to form a fine thin film and, therefore, it is necessary to form a protective film having a thickness of several hundred nanometers to several microns in order to prevent permeation of moisture or organic compounds, resulting in an increase in thermal resistance to raise the temperature of an element to thereby shorten the lifetime thereof. As described above, although it is essential to prevent the incorporation of moisture or organic compounds into a light emitting layer and electronic layers and efficiently remove the heat generated in an element for increasing the lifetime of an organic EL element and an organic EL display device, effective means have not yet been proposed.